This invention relates to glazing systems such as windows, skylights, atriums, greenhouses, sunrooms and the like.
Honeycomb transparent insulation was first developed in the early 1960""s in order to enhance the insulation value of glazed systems, with minimum loss of light transmittance. Honeycomb transparent insulation consists of transparent-walled honeycombs, with open-ended cells whose axes are oriented parallel to the normal vector of the plane of the glazing. The materials transmit light by a forward-reflection process, and impede heat transfer by suppressing convection and radiant transfer. These mechanisms are well understood and described in the technical literature. See, for example, xe2x80x9cCoupled Radiative and conductive heat transfer across honeycomb panels and through single cellsxe2x80x9d, K. G. T. Hollands et al., Int. J. Heat Mass Transfer v.27, n.11 pp. 2119-2131, 1984; xe2x80x9cAn approximate equation for predicting the solar transmittance of transparent honeycombsxe2x80x9d, K. G. T. Hollands, K. N. Marshall, and R. K. Wedel, Solar Energy, v.21 pp. 231-236, 1978).
Honeycomb transparent insulation is typically made from transparent plastics such as acrylic, polycarbonate, or polypropylene. These are manufactured by a number of different techniques, including capillary bundling, extrusion, and film-fabrication. Their properties (such as light transmittance, insulation value, rigidity, weight, etc.) strongly depend on how they were manufactured. Examples of honeycomb transparent insulations are lnsolCore(copyright), a film-based transparent insulation made by Advanced Glazings Ltd., Nova Scotia, Canada, Kapillux(copyright), a capillary-bundled transparent insulation made by Okalux Kapillarglas Gmbh. of Marktheidenfeld-Altfeld, Germany, and AREL(copyright), an extruded transparent insulation made by Arel Energy Ltd., Yavne, Israel.
It is often desirable to use honeycomb transparent insulation in a glazing unit, where it is mounted between two panes of glass, sheets of plastic, or similar, taking the place of the air gap or gas layer that traditionally provides insulation. Such glazing units can be used to let daylight into buildings, while at the same time, providing good insulation. They can be used in skylights, sunrooms, atriums, or certain window applications, or anywhere natural light is desired but a clear view of the outdoors is not necessary or desirable. The use of such honeycomb transparent insulation-filled glazing units gives the advantage of lower heat transfer (which in cold climate, causes warmer interior surface temperature, in increased thermal comfort and less condensation, and in warm climates, means lower air conditioning costs), diffuse light transmittance (resulting in high-quality uniform natural light and lower glare), and privacy.).
Rigid thick-walled honeycombs are straightforward to use in glazing units, where they are simply sandwiched in between the two sheets of glass. The rigidity of such transparent insulations prevents them from xe2x80x98saggingxe2x80x99 under their own weight, when used in inclined or vertical positions. Thus it is not necessary to fix the transparent insulation to the frame of the glazing unit or to on or both of the glazings. An example of the use of a glazing unit incorporating a rigid honeycomb transparent insulation is Okalux, made by Okalux Kappilarglas Gmbh. of Marktheidenfeld-Alffeld, Germany. This product consists of rigid capillary-bundled honeycomb transparent insulation, covered on both sides by a light diffusing fiberglass veil cloth, and sandwiched inside two pieces of clear glass, and surrounded by a spacer/frame to create a glazing unit. It is important to note that the fiberglass cloth is not bonded to the honeycomb, and is included for the purpose of diffusing light as well as for aesthetic value.
One very important parameter in determining properties of honeycomb transparent insulations is wall thickness. It is often desirable to construct honeycomb transparent insulations with the minimum practical wall thickness, because (with all other variables held constant) this results in minimum solid heat conduction, minimum optical losses, and material cost. However, the rigidity of the honeycomb is reduced as the walls become thinner. The range of practical wall thicknesses is determined to some degree by manufacturing method. The film fabrication method is known to be useful for making honeycomb transparent insulations with very thin walls. Film-fabricated honeycombs are inherently flexible, and this flexibility increases as wall thickness decreases. For example, InsolCore, a film-fabricated transparent insulation made by Advanced Glazings Ltd. of Nova Scotia, Canada, has wall thickness on the order of 0.001xe2x80x3. This flexibility can be used advantageously: such materials can be compressed to reduce volume while shipping and later re-expanded; and such materials can comply to the contours of underlying ceiling layers in ceiling-attic construction as described in our co-pending application no. CA 2,254,457.
However, flexibility becomes problematic when using honeycomb transparent insulation in applications such as daylighting, where the transparent insulation is mounted in a glazing unit between two sheets of rigid glazing material (typically glass, or plastic such as polycarbonate or acrylic). If a flexible honeycomb is simply sandwiched between glazings, as is done with rigid honeycomb transparent insulations, it is likely to sag under its own weight, drawing away from the frame at one or more edge of the glazing unit. This may be caused by gravity if the glazing unit is handled or mounted in a non-horizontal position, or it may simply happen as a result of dimensional changes caused by residual internal stresses in the honeycomb transparent insulation itself. One solution has been to attach the honeycomb to the edge (frame) of the glazing cavity, or to one or both of the rigid glazings that define the glazing unit itself. However, such a mounting procedure is labour-intensive and the use of adhesive to fasten a honeycomb to a glazing results is typically aesthetically displeasing.
It is well known that honeycomb transparent insulation scatters light and cannot transmit images at off-normal incidence. Therefore, glazing units filled with transparent insulation cannot be used in window applications where preservation of view is important. But the advantages of diffuse glazings for daylighting applications are well-known. Specifically, diffusely-transmitted light distributes throughout the interior of a building, reducing glare and shadowing relative to specularly-transmitted daylight. Filling the interior of a glazing unit with honeycomb transparent insulation contributes to the diffusing power of this glazing system. However, honeycombs are xe2x80x98conical scatterersxe2x80x99, that scatter incoming light over a range of azimuth angles, while preserving the original angle of inclination. This means that honeycomb transparent insulations have a limited ability to provide light diffusion at near-normal incidence angle. This also means that they transmit images at normal incidence, and thus a glazing unit made with specular (non-diffusing) glazings and honeycomb transparent insulation provides incomplete privacy. This is improved by the addition of one or more secondary diffusing layers, such as a loose-weave fibreglass cloth or veil, as is known in the state of the art.
The rigidity of a honeycomb material is greatly increased by bonding a sheet of material to one or both sides of the honeycomb. This principle is well-known in engineering and material science, and numerous light-weight composite honeycomb-core structural materials exist today. Examples are door panels made from wood veneer bonded to paper honeycombs, and high-tech plastic and metal honeycomb-core materials used in the aircraft industry. As well, honeycomb cores, adhesives, and skinning materials are readily available throughout the supply chain of the composites industry. The present invention takes advantage of the aforementioned principle in order to create a rigid sandwich from a flexible, thin-walled honeycomb transparent insulation core.
According to the present invention there is provided a composite light diffusing insulating glazing insert characterized in that it comprises a flexible thin-walled transparent honeycomb insulating core layer (10) defining a plurality of honeycomb cells, and a flexible skinning layer (18) bonded to each major surface of said core layer, each said flexible skinning layer having sufficient tensile and compressional stress to hold its own shape over dimensions in the order of the size of said cells whereby said composite glazing insert is substantially rigid.
The glazing insert may be in the form of honeycomb transparent insulation in glazing systems to create a light-diffusing, insulating insert that can be sandwiched between sheets of glass, plastic, or the like.
The skinning layer can be bonded to one or both sides of the insulation by means of an adhesive or by a heat-seal. The resulting covered honeycomb can be used as a diffusing, insulating glazing insert. The skinning layer may be a cloth, mesh, mat, veil, paper, or film, made from fiberglass, plastic, natural fiber, or other material.
This invention offers most of the benefits of transparent insulation itself, but also offers two additional advantages. First, the invention provides a practical way to utilize a thin-walled flexible honeycomb transparent insulation as an insulating and diffusing insert in glazing units. Second, it also provides a way to rigidize a thin-walled honeycomb transparent insulation material, so that it can hold its own dimensions prior to, and following, installation in a glazing unit. Such an insert can be used in the manufacture of diffuse insulating glazing units, in the same way as rigid transparent insulations, avoiding the problem of sag or dimensional changes inherent in the use of thin-walled flexible transparent insulations. It achieves this without the necessity of bonding the thin-walled flexible transparent insulation to the glazings or frame.
By use of this invention, the overall optical properties of the diffusing insulating glazing insert can be controlled through use of appropriate skinning layer(s). This can be used advantageously in several ways:
(a) Overall light transmittance of the insert can be reduced below that of the transparent insulation itself, as is often desirable to avoid excessive brightness in sunrooms or atriums. If a dense diffusing skinning layer is used, the insert will have lower overall light transmittance, than if a sparse high-transmittance skinning layer was used.
(b) The use of a diffuse skinning layer results in an insert with increased light diffusing power, relative to the transparent insulation itself.
(c) The use of a diffuse skinning layer results in an insert with enhanced privacy protection, relative to the honeycomb transparent insulation itself.
It is also possible to alter the thermal characteristics of the transparent insulation by using an appropriate skinning layer. In particular, the use of indium-tin-oxide coated fibreglass cloth diffusing layer or any similar cloth, film, or similar material that has low emissivity and high scattering or reflectivity in the thermal infrared, can enhance the insulation value of this invention.
The invention also provides a method of making a rigid light diffusing insulating glazing insert, characterized in that a flexible skinning layer is bonded to each major surface of a flexible thin-walled transparent honeycomb insulating core layer defining a plurality of honeycomb cells, each said flexible skinning layer having sufficient tensile and compressional stress to hold its own shape over dimensions in the order of the size of said cells so that said composite glazing insert becomes substantially rigid.